The most common and most likely answer to this crossword clue is the 10 plus 6 letter word AVOGADRO’S NUMBER
I've seen this crossword clue in The Guardian
A
V
O
G
A
D
R
O
â
€
™
S
N
U
M
B
E
R
Buddy explains!
The straight part
We know that "Thrown overboard, Magnus —/ huge figure" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case thrown overboard, magnus —/ huge figure = avogadro’s number.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.